The study of more than 53,000 middle-aged and elderly people who either once smoked or currently smoke heavily found there were 20 percent fewer deaths among those who underwent annual screening with a scanning procedure known as a low-dose helical computed tomography -- known as CT scans -- compared with those who got standard chest X-rays.

The findings were so striking that the National Cancer Institute, which helped sponsor the study, halted the National Lung Screening Trial early after a panel of experts notified officials about the clear results of an interim analysis.

"This is a study that everyone has been waiting for for a long time," said Dr. Alan Campbell, medical director of Spectrum Health's cancer program. "It's a big breakthrough. I think it will lead to more stage-one diagnoses and more surgical cures."

The lack of a good screening test is one reason the cure rate lags behind that of breast, colon and prostate cancers, Campbell said. More than 50 percent of lung cancer cases are diagnosed in stage three or four, when it usually is inoperable.

Despite the good news, local doctors said the study should not lead to annual CT scans for everyone.

The American Thoracic Society does not recommend routine screenings because they are not cost-effective, said Dr. Paul Harris, chief of pulmonary medicine at Saint Mary's Health Care.

"There have been several studies that looked at this, and none has been really convincing," he said. "I'm not sure if this study will change things."

Screenings carry risks of radiation exposure as well as false positives, which could lead to unnecessary biopsies, the doctors said. And, at this point, insurers are not willing to pay for tests for patients with no symptoms. The spiral CT scans cost $300 to $500, and X-rays cost $50 to $100, Campbell said.

But Campbell expects regular screenings will be recommended eventually for heavy smokers.